This spring, the Missouri Chamber of Commerce urged the state Legislature to accept the federal government’s plan to expand Medicaid for the poor and disabled.

The business lobbying group had not suddenly gone rogue. Here is how Daniel P. Mehan, its president, summarized his feelings about President Obama’s health care law: “We don’t like it.”

But the Chamber was cognizant of the plea of its members directly affected by the issue: dozens of Missouri hospitals stood to lose $4.2 billion over six years in federal support for uncompensated care if the state refused to increase the income ceiling for Medicaid eligibility.

Pragmatism suggested accepting the expansion. Washington would pay the extra cost entirely for three years and pick up 90 percent of the bill thereafter.

And it would expand health coverage in the state’s poor, predominantly white rural counties, which voted consistently to put Republican lawmakers into office.

After their vote, a frustrated editorial in The Missourian, a faithfully conservative newspaper in Washington, Mo., asked of the state’s elected Republicans: “Who Do They Represent?”

Today, the same forces that blocked the expansion of Medicaid in Missouri are going all out in Washington in a bid to undo all of the Affordable Care Act. Bowing to the vehemence of its Tea Party faction, the House G.O.P. forced a government shutdown when Senate Democrats refused to delay or defund the president’s health overhaul.

House Republicans are threatening even further damage if they don’t get their way, possibly unleashing financial chaos if they manage to force the United States into its first default ever on the government’s debt.

Republicans’ efforts raise the same perplexing question posed by The Missourian: What drives Tea Party Republicans and their financial backers? What calculation persuades them that repealing the health care law is worth the risk? Indeed, whose interests do they represent?

Nearly 6 in 10 Americans disapprove of trying to stop the law by cutting its financing. Even among those who don’t like the law, less than half want their representatives in Congress to try to make it fail.

It is tempting to discard the Tea Party activists driving the Republican Party as crazy — as some commentators have — motivated by fear and willing to believe that default won’t cause much harm and might even act as a purgative to free the economy of a bloated government.

“They listen to nobody but themselves,” the Harvard political scientist Theda Skocpol told me. “They are convinced of their rectitude and convinced that they alone are qualified to save America from the dire threat of Obama and his polices. They have worked themselves into a dangerous place.”

Their relationship with reality can take peculiar turns. Reflexive opponents of “government,” they can exhibit little sense of what the government actually does.

And yet the argument that half the Republican Party has simply lost its mind has to be an unsatisfactory answer, especially considering the sophistication of some of the deep-pocketed backers of the Tea Party insurgency.

There is a plausible alternative to irrationality. Flawed though it may turn out to be, Obamacare, as the Affordable Care Act is popularly known, could fundamentally change the relationship between working Americans and their government. This could pose an existential threat to the small-government credo that has defined the G.O.P. for four decades.

The law is imperfect. It has dozens of complicated, interlocking parts. Half of Americans say they don’t understand how it will affect them and their family. Still, the law has many provisions that are likely to improve life for millions of Americans, including a big portion of what we know as the working middle class.

Almost two-thirds of uninsured Americans have a full-time job, according to the Kaiser Family Foundation. A further 16 percent are employed part time.

The Department of Health and Human Services recently estimated that nearly six in 10 uninsured Americans could qualify for health coverage in the insurance market for less than $100 per person per month.

According to an analysis by the Urban Institute, 28 million Americans would gain health insurance under Obamacare. Of these, eight million earn more than twice the poverty level of $47,100 for a family of four. A majority of those would get a subsidy to buy a plan.

As it turns out, the core Tea Party demographic — working white men between the ages of 45 and 64 — would do fairly well under the law.

Take Missouri. It has about 800,000 uninsured. Almost half of them would have been eligible for expanded Medicaid benefits, had the Legislature not rejected them. Many of the rest — including families of four making up to $94,000 — will be eligible to get subsidized health insurance.

In St. Louis, for instance, a family of four making $50,000 a year will be able to buy a middle-of-the-road “silver” health plan for $282 a month and a bottom-end “bronze” plan for $32. Even Medicare recipients will get a benefit worth a few hundred dollars a year.

This could justify conservative Republicans’ greatest fears.

In 1994, when President Bill Clinton took an earlier stab at a health care overhaul, the conservative thinker William Kristol published a manifesto about why Republicans had to stop it.

“Passage of the Clinton health plan in any form would be disastrous,” Mr. Kristol wrote, italicizing for emphasis. “It would guarantee an unprecedented federal intrusion into the American economy. Its success would signal the rebirth of centralized welfare-state policy at the moment that such policy is being perceived as a failure in other areas.”

Two decades after Mr. Clinton’s ultimately failed attempt, Obamacare poses the same sort of threat.

Even Americans who say they dislike the law actually like many of its components. Nearly three-quarters approve of giving financial help to poor and moderate-income Americans to buy health insurance. Two-thirds approve of barring insurance companies from denying coverage because of somebody’s medical history. Three-quarters favor letting children stay on their parents’ insurance until they are 26.

Until now, social welfare programs in the United States have exhibited a “big hole,” Professor Skocpol said, consisting of nonpoor working-age Americans and their children. Obamacare closes a big chunk of it.

“The main beneficiaries tend to have lower wages, employed in smaller businesses that are not providing health insurance,” she said. “They are not elderly. They are also not the poorest.”

And they might be grateful to Democrats for the benefit.

To conservative Republicans, losing a large slice of the middle class to the ranks of the Democratic Party could justify extreme measures.

This actually makes a ton of sense. Expecting the usual cast of characters to post one liners basically to the effect of LALALALLALALALA!!!!!